1. Field of the Invention
The invention relates to a drag torque control method in a vehicle, additionally to a drive system.
2. Description of the Related Art
Explanation of definitions used uniformly hereafter:
Drive output P.sub.AM is the output generated by the internal combustion engine;
Drive torque M.sub.AR torque generated on the driven wheels;
Travel torque M.sub.drive is the torque which at released accelerator and with the vehicle coasting is effective, due to its kinetic energy, on the wheel and introduced in the drive train; and Drag torque M.sub.S is the torque for surmounting the entirety of resistances in the drive train which counteracts the travel torque for mechanical output transfer which includes notably the inherent friction of the internal combustion engine and transmission.
Conventionally structured automotive drive trains include at least one drive engine, notably an internal combustion engine, as well as apparatuses for torque transmission and conversion coupled to the power output. Generally, the internal combustion engine is by way of a clutch coupled to a transmission whose output may be connected to the driven wheels at least indirectly, by way of further output-transmitting components. The driver's desire for vehicle acceleration is realized via an actuating system designed, e.g., as accelerator lever or pedal. The actuating system, in turn, is coupled at least indirectly to the output actuator of the engine.
In normal operation, the wheels are driven by output transmission from the engine via the clutch and transmission to the driven wheels. However, not the entire output generated by the internal combustion engine can be transmitted to the driven wheels. A first portion of the output generated by the internal combustion engine is needed for surmounting the resistances associated with the overall system, notably the inherent resistances of the internal combustion engine and the output-transmitting components. Only the further, second portion of the output can then be utilized for acceleration or maintaining a specific vehicle speed.
The actuating system is generally coupled directly to the output actuator of the internal combustion engine, allowing the driver to express his desire for acceleration or for maintaining a specific speed. Complete release of the accelerator pedal or accelerator lever by the driver occasions an adjustment on the output actuator such that, except for the first output portion for maintaining idling operation, no further second output portion is generated. In level travel, the result is that no further drive torque is transmitted from the engine to the driven wheels. On the driven wheels, however, a travel torque is effective. This is the torque which at released accelerator pedal or accelerator lever is effective on the wheel and introduced in the drive train with the vehicle coasting, due to its kinetic energy. Part of the travel torque effective on the wheels is introduced in the drive train, causing the engine to be driven from the power output end, that is, from the wheels. This torque is counteracted by the drag torque engendered by the resistances in the drive train. Depending on the magnitude of the kinetic energy of the vehicle, the torque introduced in the drive train may serve to put the engine in deceleration, which expresses itself, however, in a reduced kinetic energy of the vehicle, that is, the travel speed. Especially in travel down an incline with the actuating system released, an increase of the drag torque counteracting the travel torque is noted, due to the kinetic energy increase of the vehicle by the effect of the gradient power output, along with an increase of the travel torque. The engine is put in drag, that is, in deceleration operation. The increasing output portion required to drive the internal combustion engine causes a drop in travel speed. At this time, the vehicle is being braked. Since the engine is in deceleration driven entirely via the drive train, an appropriately configured motor control is provided which controls the amount of fuel consumed by the engine to zero.
Drive systems with diesel electric drive configuration display a different behavior. They include an engine designed as a diesel engine, an electric machine mechanically coupled to the engine and operated as a generator, and at least one electric motor driving at least one driven wheel at least indirectly, said electric motor being coupled electrically to the electric machine. The drag torque acting on the driven wheels, such as occurring with a mechanical drive train, is in diesel electric drive systems not given automatically, due to the mechanical decoupling. Automatic fuel savings based on the travel performance are not possible, since the internal combustion engine must upon accelerator pedal release be operated at least in idling.
Therefore, an objective underlying the invention is to develop a method for influencing, respectively tuning, the drag torque of a vehicle with a drive system including an arrangement of internal combustion engine and generator, in which method a fuel-optimized travel performance analogous to conventional drive systems can be realized with means as simple as possible and at low cost. The engineering as well as control-related expense need to be kept low.